Method and system for controlling stand-by braking torque applied to automotive vehicle

ABSTRACT

The present invention pertains a method and a system for controlling a stand-by braking torque applied to an automotive vehicle under a condition of approaching or following an obstacle preceding the vehicle, the automotive vehicle having a powering system for applying a driving torque to the vehicle in response to an operator power demand. A brake controller executes a series of instructions for determining a variable indicative of dynamic situation of the vehicle, for sampling the determined values of the dynamic situation indicative variable immediately before an operator braking action to reduce the speed of the vehicle is imminent, for using the sampled values of the dynamic situation indicative variable as a basis to establish a parameter, and for using the established parameter as a basis to determine a target value of stand-by braking torque.

BACKGROUND OF THE INVENTION

The present invention relates to a method and a system for controlling astand-by braking torque applied to an automotive vehicle under acondition of approaching or following an obstacle preceding the vehicle.The term “obstacle” is used herein to mean a stationary or moving objectwithin the path of the vehicle, for example, vehicles, pedestrians, etc.

JP-A 7-144588 discloses a system whereby traveling speed anddeceleration of an obstacle preceding a host vehicle are determinedusing a Doppler sensor and a vehicle speed sensor, which are on thevehicle, and a desired distance from the obstacle is determined. In thissystem, a vehicle operator is warned and an automatic braking action isinitiated if the distance from the obstacle becomes less than thedesired distance.

Other systems have been proposed that are intended to initiate brakingaction before a vehicle operator initiates braking action. JP-A 8-80822discloses a system whereby, when the time rate of change of anaccelerator angle upon operator releasing the accelerator pedal exceedsa predetermined level, a brake actuator is activated to partiallyactivate a braking system before the foot of the operator is stepped onthe brake pedal.

The action required under such proposed procedures, whether to applystand-by braking torque, is intrusive. Inaccurate indications that thevehicle operator braking action is imminent, requiring application ofstand-by braking torque prior to the operator braking action, can reducevehicle operator satisfaction and can reduce confidence in the controlsystem. Such inaccurate indications should therefore be minimized.

Many automatic vehicle control approaches are subject to frequentinaccurate indication conditions. Such inaccurate indication conditionsmay result from modeling error. For example, mathematical modelsdetermining conditions under which stand-by braking torque is appliedmay be oversimplified, relying on broad assumptions about vehiclebehavior and operator requirements. Use of such proposed models hasresulted in limited commercial acceptance of automatic vehicle control.

An object of the present invention is to provide a method and a systemfor controlling stand-by braking torque applied to an automotive vehiclein a manner not to reduce vehicle operator satisfaction in the system.

SUMMARY OF THE INVENTION

The present invention provides a method for controlling a stand-bybraking torque applied to an automotive vehicle under a condition ofapproaching or following an obstacle preceding the vehicle, theautomotive vehicle having a powering system for applying a drivingtorque to the vehicle in response to an operator power demand, themethod comprising:

determining a variable indicative of dynamic situation of the vehicle;

sampling the determined values of the dynamic situation indicativevariable immediately before an operator braking action to reduce thespeed of the vehicle is imminent;

using the sampled values of the dynamic situation indicative variable asa basis to establish a parameter; and

using the established parameter as a basis to determine a target valueof stand-by braking torque, which is to be applied when the operatorbraking action to reduce the speed of the vehicle is imminent.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the invention will be apparent fromreading of the following description in conjunction with theaccompanying drawings.

FIG. 1 is a plan view of an obstacle avoidance situation on astraightway.

FIG. 2 is a schematic block diagram showing the arrangement of onerepresentative implementation of a system for controlling stand-bybraking torque applied to an automotive vehicle under a condition ofapproaching or following an obstacle preceding the vehicle.

FIG. 3 is a block diagram illustrating a method of the present inventionfor controlling stand-by braking torque.

FIG. 4 is a timing diagram illustrating terms (I) and (II) of formulafound by the inventors.

FIGS. 5 and 6 illustrating two different cases with the same vehiclespeed, each case having terms (I) and (II) satisfying the formula.

FIG. 7 is a block diagram illustrating a system and method for brakecontrol, which provides stand-by braking torque applied to an automotivevehicle under a condition of approaching or following an obstaclepreceding the vehicle.

FIG. 8 is a schematic sectional view of a brake actuator.

FIG. 9 is a flowchart illustrating a series of operations of a mainroutine for carrying out the preferred embodiment of this invention.

FIG. 10 is a flowchart illustrating a series of operations of asub-routine for determining setting of a stand-by braking in-progressflag (F_(PB)).

FIG. 11 is a flowchart illustrating a series of operations of asub-routine for determining a target value of hydraulic brake pressure(P_(PB)) after correcting a base value of hydraulic brake pressure(P_(PBO)).

FIG. 12 is a graph depicting a filter having various ranges of values ofa parameter in the form of maximum longitudinal acceleration (Gx_(MAX))against various values of vehicle speed (Vm).

FIG. 13 is a graph depicting various positive values of a vehicle weightgain (Km) against various values of vehicle weight (m).

FIG. 14 is a graph depicting various positive values of a road surfacefriction correction coefficient gain (Kμ) against various values of roadsurface friction coefficient (μ), i.e., coefficient of friction betweenthe road surface and the tire of at least one wheel of the automotivevehicle.

FIG. 15 is a graph depicting various positive values of a road gradientgain (Kr) against various values of road gradient (Rd).

FIG. 16 is a flowchart, similar to FIG. 9, illustrating a series ofoperations of a main routine for carrying out another preferredembodiment of this invention.

FIG. 17 is a flowchart illustrating a series of operations of asub-routine for determining a target value of brake pressure (P_(PB))after correcting a base value of brake pressure (P_(PBO)).

FIG. 18 is a graph depicting a filter having various ranges of values ofa parameter in the form of product of maximum accelerator angle andspeed ratio (F) against various values of vehicle speed (Vm).

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1 shows a typical situation on a straightway 10 having an edge 12and a centerline 14, in which a fast moving automotive vehicle 20 isapproaching an obstacle, in the form of a slow moving vehicle 22, frombehind. Vehicle 20 is moving at a velocity in the direction of an arrow24, and vehicle 22 at a velocity in the direction of an arrow 26. InFIG. 1, arrows 24 and 26 are vectors so that their lengths represent themagnitude of the velocities. In the front portion of vehicle 20, anobstacle recognition system 30, shown schematically, scans roadway 10within an angular field 32. In this case, vehicle 22 in front is locatedinside angular field 32 and vehicle 20 is spaced at a distance 34. Onthe basis of evaluation of the environmental data from detection system30, vehicle 20 will recognize the illustrated situation as a situationin which there is a need for operator braking action to reduce thevehicle speed. In this situation, it is required for the vehicleoperator to release the accelerator prior to braking action. In apreferred embodiment, control logic is employed to determine thatoperator braking action is imminent in response to a reduction inaccelerator angle in the situation in which a need for operator brakingaction remains, and to apply stand-by braking torque upon determinationthat operator braking action is imminent. Application of stand-bybraking torque is adapted for assist in vehicle operator braking action.In another embodiment, control logic may be employed to determine thatoperator braking action is imminent when speed of reduction inaccelerator angle exceeds a threshold.

FIG. 2 provides arrangement of one representative implementation of asystem for controlling stand-by braking torque in vehicle 20. The systemdetermines a target value of stand-by braking torque and a command forthe determined target braking torque. The command is applied to a brakeactuator 40. For this purpose, environmental data furnished by detectionsystem 30, vehicle condition (VC) sensors signals from vehicle condition(VC) sensors 42, and operator demand (OD) sensors signals from operatordemand sensors 44 are supplied to a brake controller 46. OD sensors 44include a sensor for detecting operator deceleration demand expressedthrough a brake pedal 48 and a sensor for detecting operator powerdemand expressed through an accelerator or accelerator pedal 50.Operator power demand is applied to a powering system 52. In theembodiment, powering system 52 is a power train including an internalcombustion engine, and a transmission. The engine has various enginespeeds and engine torques. The transmission has various speed ratiosbetween an input member driven by the engine and an output memberdrivingly coupled with at least one of wheels of vehicle 20. In apreferred embodiment, brake actuator 40 employs hydraulic fluid, such asoil, as working medium.

Referring to FIG. 3, a method of the present invention is generallyindicated at 60. At block 62, a variable indicative of dynamic situationof a vehicle is determined. In a preferred embodiment of the presentinvention, longitudinal acceleration (Gx) to which vehicle is subject tois determined as the dynamic situation indicative (DSI) variable. Inanother preferred embodiment of the present invention, accelerator angle(θ) or position is detected as DSI variable. In still another preferredembodiment of the present invention, product of (accelerator angle, θ)and (speed ratio, F) is determined as DSI variable. It will beappreciated that there is good approximation between product, θ×F. andlongitudinal acceleration, Gx, during traveling on a flat road. It willalso be appreciated that product θ×F has a good approximation to drivingtorque at the transmission output member. In other embodiment of thepresent invention, driving torque is determined as DSI variable. Instill other embodiment of the present invention, engine torque isdetermined as DSI variable.

At block 64, the determined values of DSI variable immediately beforeoperator braking action is imminent are sampled. A predetermined numberof determined values of DSI variable are sampled.

At block 66, the sampled values of DSI variable are used as a basis toestablish a parameter. In other words, the parameter is establishedbased on the sampled values of DSI variable. In a preferred embodimentof the present invention, the maximum of the sampled values is used asthe parameter.

At block 68, the established parameter is used as a basis to determine atarget value of stand-by braking torque. In other words, a target valueof stand-by braking torque is determined based on the establishedparameter.

It is to be appreciated that the language “established parameter” ismeant to encompass also other parameter resulting from appropriateprocessing and/or evaluation of the sampled values of DSI as long as itrepresents significant characteristic of vehicle dynamic situation,which actively induces operator anticipation of longitudinaldeceleration of a vehicle upon releasing accelerator.

Extensive study conducted by the inventors have led them to find aninventive formula governing Gx_(MAX), D_(EBT), and D_(SBBT),

where, Gx_(MAX) represents magnitude of the selected maximumacceleration value before determination that operator braking action isimminent;

D_(EBT) represents magnitude of longitudinal deceleration due to enginebraking torque upon the determination that operator braking action isimminent;

D_(SBBT) represents magnitude of magnitude of longitudinal decelerationdue to stand-by braking torque applied upon the determination thatoperator braking action is imminent.

With reference to FIG. 4, the formula can be expressed as:

(Gx _(MAX) +D _(EBT) +D _(SBBT))/(Gx _(MAX) +D _(EBT))=II/I≦α  (1),

where:

II represents the term (Gx_(MAX)+D_(EBT) +D_(SBBT));

I represents the term (Gx_(MAX)+D_(EBT)); and

α is a value greater than 1 (one) and may take different values fordifferent types of vehicles, respectively.

Formula (1) expresses condition under which addition of D_(SBBT) willmeet with much acceptance by vehicle operator even in situations thatthe operator would have negotiated without resorting to depression ofbrake pedal. In plain words, with D_(SBBT) satisfying formula (1), it islikely that vehicle operator will not experience such additionaldeceleration due to application of stand-by braking torque as distinctfrom deceleration due to engine braking torque.

With reference to FIGS. 5 and 6, cases with different magnitudes ofGx_(MAX) are considered. With the same vehicle speed, determination thatoperator braking action is imminent is made in each of the cases.Magnitude D_(EBT) remains the same in each of the cases irrespective ofvariation in magnitude Gx_(MAX). Hence, applying formula (1) in each ofthe cases will provide that magnitude D_(SBBT) may be increased inproportional relationship to magnitude Gx_(MAX). The magnitude Gx_(MAX)is greater in FIG. 6 than that in FIG. 5 so that the magnitude D_(SBBT)in FIG. 6 is greater than that in FIG. 5.

Referring to FIG. 7, a block diagram illustrates an operation of asystem or method for controlling stand-by braking torque applied to anautomotive vehicle under a condition of approaching or following anobstacle preceding the vehicle. System 100 preferably includes acontroller, such as brake controller 46. Brake controller 46 comprises amicroprocessor-based controller associated with a microprocessor,represented by a reference numeral 102. Microprocessor 102 communicateswith associated computer-readable storage medium 104. As will beappreciable by one of ordinary skill in the art, computer-readablestorage medium 104 may include various devices for storing datarepresenting instructions executable to control a braking system. Forexample, computer-readable storage medium 104 may include a randomaccess memory (RAM) 106, a read-only memory (ROM) 108, and/or akeep-alive memory (KAM) 110. These functions may be carried out throughany one of a number of known physical devices including EPROM, EEPROM,flash memory, and the like. The present invention is not limited to aparticular type of computer-readable storage medium, examples of whichare provided for convenience of description only.

Brake controller 46 also includes appropriate electronic circuitry,integrated circuits, and the like to effect control of the brakingsystem. As such, controller 46 is used to effect control logicimplemented in terms of software (instructions) and/or hardwarecomponents, depending upon the particular application. Details ofcontrol logic implemented by controller 46 are provided with referenceto FIGS. 3, 9-11, and 16-17.

Controller 46 preferably receives inputs from brake actuator 40indicative of present conditions of the brake actuator 40. For example,controller 46 may receive brake system pressure indicative of apneumatic or hydraulic pressure for operating one or more brakingdevices, which may include any device that applies a negative torque tofront wheels 112 and 114 and rear wheels 116 and 118. A braking deviceincludes various types of friction brakes, such as disk brakes 120, 122,124, and 126 or drum brakes. In the embodiment shown in FIG. 7, apressure sensor 128 is provided to detect brake pressure Pw delivered tofriction brakes 120 and 122 for front wheels 112 and 114. In theembodiment, a brake actuator 40 includes a master brake cylinder 130,with a brake booster 208, and a brake pedal 48. Pressure sensor 128 islocated to detect brake pressure Pw within hydraulic fluid lineinterconnecting master brake cylinder 130 and friction brakes 120 and122. Brake booster 208 in the embodiment is described later inconnection with FIG. 8.

Controller 46 receives inputs from operator demand sensors 44, whichinclude a brake switch 132 and an accelerator stroke (AC) sensor 134.The setting is such that brake switch 132 is turned off upon operatorreleasing brake pedal 48 or turned on upon operator depressing brakepedal 48. AC sensor 134 detects angle θ of accelerator pedal 50 throughmeasurement of its stroke. Controller 46 receives angle θ and determinesoperator power demand expressed through accelerator pedal 50. In theembodiment, AC sensor 134 constitutes a component of a system fordetermining the magnitude or degree of operator power demand.

In the embodiment shown in FIG. 7, controller 46 receives input SW froma stand-by braking mode (SBBM) switch 136, which may be manuallyoperated or automatically operated in view of circumstances around thevehicle 20. The setting is such that controller 46 performs operation instand-by braking mode upon selection of the mode by SBBM switch 136.

Controller 46 receives environmental data from obstacle detection system30. In the embodiment shown in FIG. 7, obstacle detection system 30includes a radar sensor in the form of a conventional laser radar or amillimeter wave (MMW) radar sensor mounted in a forward section ofvehicle 20. The conventional laser radar sensor comprises such knownelements as laser diodes, transmission and receiver lenses, infraredfilters, and photodiodes, as is generally understood in the art to whichthis invention pertains. MMW radar typically comprises such knownelements as an antenna, down converter, video processor, FMCW modulatorand associated electronics, as is generally understood in the art towhich this invention pertains. The radar sensor propagates a signalalong the path of vehicle 20 and collects reflections of the signal froman obstacle in or near the path. Obstacle detection system 30 furthercomprises an analog-to-digital converter of any suitable conventionaltype for converting the radar sensor output signal to a digital form forprocessing in microprocessor 102 to determine a distance L betweenvehicle 20 and an obstacle preceding the vehicle or a range to theobstacle.

Controller 46 receives input from a vehicle speed sensor 138. Vehiclespeed sensor 138 is provided to measure or detect speed of rotation ofthe transmission output member. The vehicle speed sensor output signalis converted to a digital form by a suitable conventionalanalog-to-digital converter for processing in microprocessor 102 todetermine vehicle speed Vm of vehicle 20. Most current vehicles areprovided with a microprocessor-based controller, such as, an enginecontroller or an automatic transmission controller, which processesinput from a vehicle speed sensor to determine vehicle speed Vm. In suchcase, controller 46 may receive the determined vehicle speed from suchcontroller.

Controller 46 receives inputs from a vehicle weight detection system140, which includes load sensors mounted to vehicle suspension system.Each of the load sensor output signals is converted to a digital form bya suitable conventional analog-to-digital converter for processing inmicroprocessor 102 to determine vehicle weight m of vehicle 20.

In the embodiment, controller 46 receives input from a system 142 fordetermining longitudinal acceleration, which vehicle 20 is subject to.Longitudinal acceleration determining system 142 may comprise anaccelerometer. However, most current vehicles are not provided withaccelerometers. In the embodiment, the system 142 comprises softwareoperations in a microprocessor to determine the time rate change ofvehicle speed Vm for use as longitudinal acceleration Gx. In theembodiment, the determined value of longitudinal acceleration Gx is usedas DSI variable, which is determined at block 62 in FIG. 3.

In another embodiment of the present invention, the controller 46receives input from AC sensor 134, and determines accelerator angle θ.The determined value of accelerator angle θ is used as DSI variablebecause it (θ) varies in a pattern similar to pattern of variation oflongitudinal acceleration Gx.

In other embodiment of the present invention, controller 46 receivesinput from a conventional inhibitor switch 144 coupled to a selectlever, as indicated at block 146, of the transmission of powering system52. Select lever 146 has various positions including park “P”, drive“D”, neutral “N” and reverse “R”. Inhibitor switch 144 generates outputsindicative of the various positions selectable by select lever 146. Mostcurrent vehicles are provided with microprocessor-based controllers fortransmissions. Such controllers compute a speed ratio between rotationalspeed of an input shaft of a transmission and rotational speed of anoutput shaft of the transmission. Controller 46 communicates with atransmission controller, as indicated by a block 148, for thetransmission of powering system 52 to receive a speed ratio F betweentransmission input and output shafts. Controller 46 determines orcomputes a product of (accelerator angle, θ) and (speed ratio, F) anduses the determined value of the product θ×F as DSI variable.

As environmental data, controller 46 uses the coefficient of friction(μ) between the road surface and the tire of at least one wheel ofvehicle 20 (road friction coefficient μ) and the gradient (Rd) of theroad surface (road gradient Rd). A system 150 for determining roadfriction coefficient μ uses sensor data to determine road frictioncoefficient μ. Controller 46 may receive input from road frictioncoefficient determining system 150 or sensor data to determine roadfriction coefficient μ. A system 152 for determining road gradient Rduses sensor data to determine road gradient Rd. Controller 46 mayreceive input from road gradient determining system 152 or sensor datato determine road gradient Rd.

In the embodiments of the present invention, processor 102 of controller46 effects processing input data to determine a target value of brakepressure to accomplish a target value of stand-by braking torque andapplies a command to brake booster 208.

Referring to FIG. 8, brake booster 208 includes an electro-magneticallyoperable control valve arrangement 240. Controller 46 provides brakingcommand or signal to control valve arrangement 240 for adjustment ofbrake pressure to accomplish a target value of stand-by braking torque.Brake booster 208 comprises an essentially rotation symmetrical housing242, in which a rear chamber 244 and a front chamber 246 are arrangedand separated from each other by a movable wall 248. Control valvearrangement 240 is coupled with movable wall 248 for a common relativemovement with respect to housing 242. The front end of rod-shapedactuation member 220, which is coupled with brake pedal 48, acts oncontrol valve arrangement 240.

Within brake booster 208, a power output member 250 is arranged whichbears against control valve arrangement 240. Power output member 250 isprovided for activation of master brake cylinder 130.

Control valve arrangement 240 comprises an essentially tubular valvehousing 252. The front end of valve housing 252 is coupled to movablewall 248. A return spring 254 arranged within brake booster 208resiliently biases the control valve arrangement 240 rearwardly. Withinvalve housing 252, an electromagnetic actuator 300 is arranged whichincludes a solenoid coil 300 a and a plunger 300 b. Arranged withinplunger 300 b is an operating rod 302. The front end of operating rod302 bears against power output member 250. A return spring 304 locatedwithin plunger 300 b has one end bearing against a retainer (no numeral)fixedly connected to plunger 300 b and opposite end bearing against therear end of operating rod 302 The front ball end of rod-shaped actuator220 is fixedly inserted into socket recessed inwardly from the rear endof operating rod 302. A return spring 306 located within valve housing308 has one end bearing against a shoulder of valve housing 308 andopposite end bearing against a shoulder of rod-shaped actuator 220.

Valve housing 308 is formed with a passage 310 through which fluidcommunication between rear and front chambers 244 and 246 isestablished. The front end of passage 310 is always open to frontchamber 246, while the rear end of passage 310 is located within a valveseat 312. Valve seat 312 is located within an annular space definedbetween plunger 300 b and valve housing 308 and faces a valve member 314that forms an upper portion of a slide. The slide is located betweenplunger 300 b and valve housing 308. A return spring 316 has one endbearing against an integral abutment 318 of plunger 300 b and oppositeend bearing against the slide. An air admission port 320 is formedthrough a lower portion of the slide. This lower portion of the slideserves as a valve seat 322. Port 320 is provided to admit ambient airinto rear chamber 244. Valve seat 322 formed with port 320 faces a valvemember 324 integral with plunger 300 b. Valve seat 312 and valve member314 cooperate with each other to form an interruption or vacuum valve.Valve seat 322 and valve member 324 cooperate with each other to form anambient air admission valve.

In the rest position shown in FIG. 8 with the vacuum sourcedisconnected, atmospheric pressure prevails in both chambers 244 and246. With the vacuum source connected, i.e., with the engine running, avacuum builds up in front chamber 246 so that movable wall 248 togetherwith the control valve arrangement 240 is slightly displaced in aforward direction. Accordingly, a new pressure balance is achievedbetween two chambers 244 and 246. From this position, a lost travel freeactivation of the brake booster 208 is ensured.

Under a normal brake actuation by the vehicle operator, the brakebooster 208 operates in a usual manner by interrupting the connectionbetween two chambers 244 and 246 via the interruption valve (312, 314)and admitting ambient air into rear chamber 244 via the ambient airadmission valve (324, 322).

Electromagnetic actuator 300 can actuate control valve arrangement 240.For this purpose, current through solenoid 300 a is regulated inresponse to the command furnished by brake controller 46. This commandcauses a displacement of control valve arrangement 240 so that ambientair can flow into rear chamber 244.

With reference to FIG. 7, a series of operations are stored in computerreadable storage media 104 in the form of sequences of instructionsimplemented in software for determining DSI variable, sampling thedetermined values of DSI variable immediately before operator brakingaction is imminent, using the sampled values of DSI variable as a basisto establish a parameter, and using the established parameter as a basisto determine a target value of stand-by braking torque.

FIGS. 9, 10 and 11 illustrate a series of operations for carrying out apreferred embodiment of this invention. The process steps of FIGS. 9-11are periodically executed in brake controller 46 when stand-by brakingmode is selected by SMMB switch 136 (see FIG. 7) after the ignition hasbeen on and electric power has been applied to controller 46.

In FIG. 9, a main control routine is generally indicated at 400. In FIG.10, a sub-routine is generally indicated at 420. In FIG. 11, asub-routine is generally indicated at 440.

The process steps of FIGS. 9-11 are carried out every ΔT (for example,10 milliseconds) in controller 46 as provided through a standardcomputer timer-based interrupt process.

Each sequential execution of the microprocessor operations of FIG. 9begins at “START” block and proceeds to process block 402. In block 402,the processor inputs or receives output signals from sensors, includingpressure sensor 128, AC sensor 134 and vehicle speed sensor 138, fromswitches, including brake switch 132, SBBM switch 136, and from systems,including obstacle detection system 30, vehicle weight detection system140, acceleration determining system 142, road friction coefficient (μ)determining system 150, and road gradient (Rd) determining system 152.The determined value of longitudinal acceleration Gx is stored as thenewest one of a predetermined number of stored data after moving asequence of the stored data to the right or left by overflowing theoldest one of the stored data. In the embodiment, the predeterminednumber of stored data is forty and the forty stored data are representedby Gx₀, Gx₋₁, Gx₋₂, . . . Gx₋₃₉, respectively. Gx₀ represents the neweststored datum, and Gx₋₃₉ represents the oldest stored datum. Morespecifically, the determined value Gx in the present operation cycle isstored as Gx₀. The forty stored data are processed in block 404. Inblock 404, the processor carries out a standard process of selecting ordetermining the maximum among the forty stored data Gx₀, Gx₋₁, Gx₋₂, . .. Gx₋₃₉ to update a maximum longitudinal acceleration Gx_(MAX).Processing at block 404 provides the maximum Gx_(MAX) among fortysampled determined values of longitudinal acceleration, which have beensampled over a period of time of 400 milliseconds that ends withbeginning of each sequential execution of the microprocessor operations.

After updating Gx_(MAX), determined values of vehicle speed Vm anddistance L are next processed at block 406. At process block 406, theprocessor calculates the time rate of change in distance dL/dt (relativespeed between vehicle and the preceding obstacle) and a thresholddistance L₀, which is expressed as:

L ₀ ={Vm ²−(Vm−dL/dt)²}/2G _(D)  (2),

where:

Vm represents the determined value of vehicle speed;

L represents the determined value of distance between vehicle and anobstacle preceding the vehicle; and

G_(D) represents a predetermined absolute value of vehicle longitudinaldeceleration, this predetermined absolute value being less than themaximum of absolute values of vehicle longitudinal deceleration, whichmay be induced by operator braking action for emergency braking, butbeing as great as absolute value of vehicle longitudinal deceleration,which may be induced by operator braking action for normal braking.

The process then proceeds to block 408. In block 408, distance L andthreshold L₀are compared. In this query, if L is less than or equal toL₀(answer “YES”), the process proceeds to block 410 and execution ofsub-routine 420 (see FIG. 10) begins. In the query at block 408, if L isgreater than L₀(answer “NO”), the process proceeds to block 412, andprocesses are carried out to stop command from controller 46 to releasebrake booster 208. After block 412, the process skips to “RETURN” block.In the embodiment, the query at block 408 is utilized as an analysis todetermine whether there is a need for operator braking action to avoid apotential problem to the vehicle posed by an obstacle preceding thevehicle. If the analysis at block 408 concludes that the obstaclepreceding the vehicle poses a potential problem to the vehicle, theprocess advances to block 410 to proceed to blocks 422-438 ofsub-routine 420 in FIG. 10 where further analysis is commenced.

Referring to FIG. 10, microprocessor operations at blocks 422-438 arecarried out to determine whether operator braking action is imminent toavoid the potential problem. This further analysis utilizes acceleratorangle θ as operator power demand information. Alternatively, in theplace of accelerator angle θ, a throttle position or a pulse width offuel injection pulse may be utilized. In block 422, a stand-by brakingin-progress flag F_(PB) is checked. In query at block 422, if flagF_(PB) is cleared or reset (answer “YES”), the process moves to block424, and an accelerator wide-open flag F_(OP) is checked. In query atblock 422, if flag F_(PB) is set (answer “NO”), the process moves toblock 426, and accelerator angle θ and a predetermined accelerator openthreshold angle θ_(OP) are compared.

In query at block 424, if flag F_(OP) is cleared or reset (answer“YES”), the process proceeds to block 428, and accelerator angle θ andthreshold angle θ_(OP) are compared. In query at block 424, if flagF_(OP) is set (answer “NO”), the process skips to block 432.

In query at block 428, if accelerator angle θ is greater than or equalto threshold angle θ_(OP) (answer “YES”), the process proceeds to block430, and flag F_(OP) is set. Next, the process proceeds to block 432. Inquery at block 428, if accelerator angle θ is less than θ_(OP) (answer“NO”), the process skips to block 432.

In block 432, flag F_(OP) is checked. In query at block 432, if flagF_(OP) is set (answer “YES”), the process proceeds to block 434, andaccelerator angle θ and an accelerator close threshold angle θ_(OFF) arecompared. Threshold angle θ_(OFF) is less than θ_(OP). In query at block432, if flag F_(OP) is cleared or reset (answer “NO”), the process skipsto block 414 of main routine 400 in FIG. 9.

In query at block 434, if accelerator angle θ is less than or equal toθ_(OFF) (answer “YES”), the process proceeds to block 436, and flagF_(PB) is set and flag F_(OP) is cleared or reset. Then, the processskips to block 414 in FIG. 9. In query at block 434, if acceleratorangle θ is greater than θ_(OFF) (answer “NO”), the process skips toblock 414 of main routine 400 in FIG. 9.

In query at block 426, if accelerator angle θ is less than or equal toθ_(OP) (answer “YES”), the process skips to block 414 of main routine400 in FIG. 9. In query at block 426, if accelerator angle θ is greaterthan θ_(OP) (answer “NO”), the process proceeds to block 438, and flagF_(PB) is cleared or reset. Then, the process skips to block 414 of mainroutine 400 in FIG. 9. As is readily understood by those skilled in theart to which this invention pertains, flag F_(PB) is set upondetermination that operator braking action is imminent (flow alongblocks 422-424-432-434-436), and subsequently cleared or reset upondetermination that accelerator angle θ has exceeded threshold angleθ_(OP) (flow along blocks 422-426-438).

From the preceding description, it is now understood that, in theembodiment, the process determines that operator braking action isimminent upon a reduction of accelerator angle θ from θ_(OP) to θ_(OFF)(flow along blocks 423-430-432-434-436) under a condition that L≦L_(O)(flow along blocks 408-410).

Turning back to FIG. 9, at process block 414, flag F_(PB) is checked. Inquery at block 414, if flag F_(PB) is set (answer “YES”), the processproceeds to block 416, and microprocessor operations at blocks 442-464of sub-routine 440 (FIG. 11) are carried out. In query at block 414, ifflag F_(PB) is cleared or reset (answer “NO”), the process proceeds toblock 412, and processes to stop command are carried out. After block416 or 412, the process skips to “RETURN” block.

Referring to FIG. 11, microprocessor operations at blocks 442-464 arecarried out to determine a target value P_(PB) of brake pressure basedon a parameter in the form of maximum longitudinal accelerationGx_(MAX). The parameter Gx_(MAX) has been established based on fortystored data Gx₀, Gx₋₁, Gx₋₂, . . . Gx₋₃₉. These data were sampled over aperiod of time of 400 milliseconds that ends with an operation cyclewhere determination that operator braking action is imminent is firstmade. More specifically, at block 442, a stand-by braking start-up flagF_(ST) is checked. Flag F_(ST) is set after execution of the initialoperation cycle of sub-routine 440. In query at block 442, if flagF_(ST) is cleared or reset (answer “YES”), the process proceeds to block444 and a base value P_(PBO) of brake pressure is determined againstGx_(MAX) and vehicle speed Vm. The process then moves to block 446 andflag F_(ST) is set. The process proceeds next to block 448. In query atblock 442, if flag F_(ST) has been set (answer “NO”), the process skipsto block 448. As flag F_(ST) is initially reset, but it is setafterwards after determination of P_(PBO) at block 444, the processskips from block 442 to block 448 during each of the subsequentoperation cycles of sub-routine 440. The base value P_(PBO) determinedat block 444 remains unaltered during the subsequent operation cycles.

With reference to FIG. 12, description is made on how to determine, atblock 444 in the embodiment, an appropriate base value P_(PBO) usingparameter Gx_(MAX) and vehicle speed Vm. FIG. 12 is a graph depicting afilter having various ranges of values of a parameter in the form ofmaximum longitudinal acceleration Gx_(MAX) against various values ofvehicle speed Vm. Lines S1 and S2 illustrate variations of upper andlower extreme values of the ranges of the filter. As indicated by linesS1 and S2, upper and lower extreme values remain as high asGx_(MAX Hi-U) and Gx_(MAX Hi-L), respectively, against various values ofvehicle speed Vm lower than or equal to Vm_(Lo), while they remain ashigh as Gx_(MAX Lo-U) and Gx_(MAX Lo-L), respectively, against variousvalues of vehicle speed Vm higher than or equal to Vm_(Hi). Againstintermediate values of vehicle speed Vm between Vm_(Lo) and Vm_(Hi), thelines S1 and S2 have ramp-like sections, respectively. The ramp-likesection of line S1 interconnects a level as high as Gx_(MAX Hi-U) and alevel as high as Gx_(MAX Lo-U). The ramp-like section line S2interconnects a level as high as Gx_(MAX Hi-L) and a level as high asGx_(MAX Lo-L). The relationship is such that Vm_(Hi)>Vm_(Lo). Therelationship is such that

Gx _(MAX Hi-U) >Gx _(MAX Hi-L) >Gx _(MAX Lo-U) >Gx _(MAX Lo-L),

and

(Gx _(MAX Hi-U) −Gx _(MAX Hi-L))>(Gx _(MAX Lo-U) −Gx _(MAX Lo-L)).

As is readily seen from FIG. 12, the filter has a wide range, whichcovers relatively large values of parameter Gx_(MAX), when Vm is lessthan or equal to Vm_(Lo), while it has a narrow range, which coversrelatively small values of parameter Gx_(MAX), when Vm is greater thanor equal to Vm_(Hi). As Vm increases from Vm_(Lo) to ward Vm_(Hi), therange of filter gradually becomes narrow and the coverage by the filterrange shifts.

If a determined value of parameter Gx_(MAX) is greater than an upperextreme value, i. e., a point on line S1, selected against a determinedvalue of vehicle speed Vm, a maximum base value P_(PBO MAX) is set asbase value P_(PBO). If a determined value of parameter Gx_(MAX) is lessthan a lower extreme value, i.e., a point on line S2, selected against adetermined value of vehicle speed Vm, a minimum base value P_(PBO MIN)is set as base value P_(PBO). In the embodiment, the setting is suchthat the maximum base value P_(PBO MAX) is 0.5 MPa and the minimum basevalue P_(PBO MIN) is 0.1 MPa.

Let us consider the case where a determined value of parameter Gx_(MAX)is less than or equal to an upper extreme value, i.e., a point on lineS1, selected against a determined value of vehicle speed Vm, but greaterthan or equal to a lower extreme value, i.e., a point on line S2,selected against the determined value of vehicle speed Vm. In this case,the base value P_(PBO) is determined by calculating the equation asfollows:

P _(PBO)=(P _(PB MAX) −P _(PB MIN))×(Gx _(MAX) *−Gx _(MAX-L))÷(Gx_(MAX U) −Gx _(MAX-L))+P_(PB MIN)  (3),

where:

Gx_(MAX-U) is a general representation of an upper extreme value of arange of the filter selected against a determined value of vehicle speedVm;

Gx_(MAX-L) is a general expression of a lower extreme value of therange; and

Gx_(MAX)* represents a determined value of parameter in the form ofmaximum longitudinal acceleration that falls in the range having theupper and lower extreme values Gx_(MAX-U) and Gx_(MAX-L).

In a stored look-up table in computer readable storage medium 104, upperand lower extreme values Gx_(MAX-U) and Gx_(MAX-L) are arranged orallocated against various values of vehicle speed Vm in a manner asillustrated by the upper and lower threshold lines S1 and S2 illustratedin FIG. 12. In the embodiment, this look-up table is used formicroprocessor operations at block 444 in FIG. 11.

Referring back to FIG. 11, at block 444, the processor determines basevalue P_(PBO) of brake pressure through microprocessor operations, whichinclude:

1) Performing a table look-up operation of the above-mentioned look-uptable using a determined value of vehicle speed Vm to find or determineupper and lower extreme values Gx_(MAX-U) and Gx_(MAX-L) of a rangeappropriate to the determined value of vehicle speed Vm;

2) Comparing a determined maximum longitudinal acceleration Gx_(MAX) tothe determined upper and lower extreme values Gx_(MAX-U) and Gx_(MAX-L);

3) In the case (A) where Gx_(MAX-U)≧Gx_(MAX)≧Gx_(MAX-L), determiningbase value P_(PBO) by calculating the equation (3);

4) In the case (B) where Gx_(MAX)<Gx_(MAX-L), setting thatP_(PBO)=P_(PBO MIN); and

5) In the case (C) where Gx_(MAX)>Gx_(MAX-U), setting thatP_(PBO)=P_(PBO MAX).

After microprocessor operations at block 444, the process advances toblock 446 and then to block 448. At block 448, an appropriate value ofvehicle weight gain Km is determined against a determined value ofvehicle weight m by using a look-up table as illustrated by the fullydrawn line in FIG. 13. The value of vehicle weight m is obtained atblock 402 (see FIG. 9). Further description on this look-up table ismade later with reference to FIG. 13. The process then moves to block450.

At block 450, the processor determines a current value of road surfacefriction coefficient μ. Information on longitudinal acceleration Gx orlateral acceleration, which the vehicle is subject to, may be used formicroprocessor operations to estimate or calculate road frictioncoefficient μ. The process then goes to block 452. At block 452, anappropriate value of road surface friction coefficient gain Kμ isdetermined against the determined value of road friction coefficient μby using a look-up table as illustrated by the fully drawn line in FIG.14. Further description on this look-up table is made later withreference to FIG. 14. The process then moves to block 454.

At block 454, the processor determines a current value of road gradientRd. Information from sensor data may be used for microprocessoroperations to estimate or calculate road gradient Rd. The process movesnext to block 456. At block 456, an appropriate value of road gradientgain Kr against the determined value of road gradient Rd by using alook-up table as illustrated by the fully drawn line in FIG. 15. Furtherdescription on this look-up table is made later with reference to FIG.15. The process then moves to block 458.

At block 458, the processor determines a target value of brake pressureP_(PB) to accomplish a target value of stand-by braking torque bycalculating an equation as follows:

 P _(PB) =Km×Kμ×Kr×P _(PBO)  (4),

where:

a product (Km×Kμ×Kr) represents a combined gain.

The process moves to next block 460. At block 460, the processordetermines a command for accomplishing target value P_(PB) and issuesthe command toward electromagnetic actuator 300 of brake booster 208(see FIG. 7). Then, the process proceeds to block 462, and a brakeswitch output S_(BRK) from brake switch 132 is checked. In query atblock 462, if brake switch output S_(BRK) is equal to “1” (answer“YES”), the process goes to block 464. In query at block 462, if brakeswitch output S_(BRK) is “0” (answer “NO”), the process skips to“RETURN” block of main routine 400 (see FIG. 9). At block 464, bothflags F_(PB) and F_(ST) are cleared. The process returns to “RETURN”block of main routine 400. The relationship between brake switch outputS_(BRK) and brake switch 132 is such that if brake pedal 48 isdepressed, brake switch 132 is turned on and brake switch output S_(BRK)is equal to “1”, and if brake pedal 48 is not depressed, brake switch132 is turned off and brake switch output S_(BRK) is equal to “0”.

With reference to FIG. 13, the fully drawn line illustrates variation ofvehicle weight gain Km. The vertical axis represents various values ofvehicle weight gain Km and the horizontal axis represents various valuesof vehicle weight m. A range of values, which Km may take, has an upperextreme value Km_(Hi), a lower extreme value Km_(Lo), and intermediatevalues. In the embodiment, the upper extreme value Km_(Hi) is 1.0, andthe lower extreme value Km_(Lo) is 0.1. The illustrated fully drawn lineremains as high as upper extreme value Km_(Hi) against various values ofvehicle weight Vm lower than or equal to a predetermined low vehicleweight value m_(Lo), while it remains as high as lower extreme valueKm_(Lo) against various values of Vm higher than or equal to apredetermined high vehicle weight value m_(Hi). Against intermediatevalues between m_(Lo) and m_(Hi), the fully drawn line has a ramp-likesection. This ramp-like section interconnects a level as high as Km_(Hi)and a level as high as Km_(Lo). As clearly indicated by the ramp-likesection of the fully drawn line, the intermediate values of Km have alinear inverse proportional relationship with the intermediate values mbetween m_(Lo) and m_(Hi). It is now appreciated that vehicle weightgain Km decreases as vehicle weight m increases to reflect adeceleration performance characteristic that the magnitude ofdeceleration, induced due to application of a braking torque, decreasesas vehicle weight m increases. As indicated in equation (4), multiplyinggain Km with base value P_(PBO) results in incorporating thischaracteristic into target value P_(PB).

With reference to FIG. 14, the fully drawn line illustrates variation ofroad surface friction coefficient gain Kμ. The vertical axis representsvarious values of gain Kμ and the horizontal axis represents variousvalues of road surface friction coefficient μ. A range of values, whichKμ may take, has an upper extreme value Kμ_(Hi), a lower extreme valueKμ_(Lo), and intermediate values. In the embodiment, the upper extremevalue Kμ_(Hi) is 1.0, and the lower extreme value Kμ_(Lo) is 0.1. Theillustrated fully drawn line remains as high as lower extreme valueKμ_(Lo) against various values of road surface friction coefficient μlower than or equal to a predetermined low road friction coefficientvalue μ_(Lo), while it remains as high as upper extreme value Kμ_(Hi)against various values of μ higher than or equal to a predetermined highroad friction coefficient value μ_(Hi). Against intermediate valuesbetween μ_(Lo)and μ_(Hi), the fully drawn line has a ramp-like section.This ramp-like section interconnects a level as high as Kμ_(Lo) and alevel as high as Kμ_(Hi). As clearly indicated by the ramp-like sectionof the fully drawn line, the intermediate values of Kμ have a linearproportional relationship with the intermediate values of μ betweenμ_(Lo) and μ_(Hi). It is now appreciated that gain Kμ decreases as roadsurface friction coefficient μ decreases to reflect a decelerationcharacteristic that the magnitude of deceleration, induced due toapplication of a braking torque, decreases as road surface frictioncoefficient μ decreases. As indicated in equation (4), multiplying thegain Kμ with base value P_(PBO) results in incorporating thischaracteristic into target value P_(PB).

With reference to FIG. 15, the fully drawn line illustrates variation ofroad gradient gain Kr. The vertical axis represents various values ofgain Kr and the horizontal axis represents various values of roadgradient Rd. A range of values, which Kr may take, has an upper extremevalue Kr_(Hi), a lower extreme value Kr_(Lo), and intermediate values.The intermediate values include a middle value Kr_(Md). In theembodiment, the upper extreme value Kr_(Hi) is 1.0 and the lower extremevalue Kr_(Lo) is 0.1. Road gradient Rd takes a positive value if road isascending, but takes a negative value if road is descending. In the casewhere ascending is low in degree, positive values of road gradient Rdare less than or equal to a predetermined low ascending range boundaryvalue Rd_(Lo-C). In the case where descending is low in degree, negativevalues of road gradient Rd are greater than or equal to a predeterminedlow descending range boundary value Rd_(Lo-D) . In the case whereascending is high in degree, positive values of road gradient Rd aregreater than or equal to a predetermined high ascending range boundaryvalue Rd_(Hi-C). In the case where descending is high in degree,negative values of road gradient Rd are less than or equal to apredetermined high descending range boundary value Rd_(Hi-D). Theillustrated fully drawn line remains as high as low extreme valueKr_(Lo) against varying negative values of road gradient Rd less than orequal to Rd_(Hi-D), while it remains as high as high extreme valueKr_(Hi) against varying positive values of road gradient Rd greater thanor equal to Rd_(Hi-C). Against various values of road gradient Rd, whichare greater than or equal to Rd_(Lo-D) but less than or equal toRd_(Lo-C), the fully drawn line remains as high as middle value Kr_(Md).Against intermediate positive values between Rd_(Lo-C) and Rd_(Hi-C),the fully drawn line has a first ramp-like section. This ramp-likesection interconnects a level as high as Kr_(Md) and a level as high asKr_(Hi). As clearly indicated by the first ramp-like section, theintermediate values of Kr between Kr_(Md) and Kr_(Hi) have a linearproportional relationship with the intermediate positive values of Rdbetween Rd_(Lo-C) and Rd_(Hi-C). Against intermediate negative valuesbetween Rd_(Lo-D) and Rd_(Hi-D), the fully drawn line has a secondramp-like section. This second ramp-like section interconnects a levelas high as Kr_(Md) and a level as high as Kr_(Lo). As clearly indicatedby the second ramp-like section, the intermediate values of Kr betweenKr_(Md) and Kr_(Lo) have a linear proportional relationship with theintermediate negative values between Rd_(Lo-D) and Rd_(Hi-D). It is nowappreciated that gain Kr increases as road gradient Rd increases inascending road to reflect a deceleration characteristic that themagnitude of deceleration, induced due to application of a brakingtorque, increases in ascending road as road gradient Rd increases. GainKr decreases as the absolute value of road gradient Rd increases indescending road to reflect a deceleration characteristic that themagnitude of deceleration, induced due to application of a brakingtorque, decreases in descending road as the absolute value of roadgradient Rd increases. As indicated in equation (4), multiplying thegain Kr with base value P_(PBO) results in incorporating thesecharacteristics into target value P_(PB).

From the preceding description of the embodiment particularly withreference to FIGS. 4-6 and 12, it is now appreciated that the base valueP_(PBO) takes intermediate values between the minimum and maximum basevalues P_(PBO MIN) and P_(PBO MAX). The intermediate values have alinear proportional relationship with values of parameter Gx_(MAX)* thatfall in a range of the filter having upper and lower extreme valuesGx_(MAX-U) and Gx_(MAX-L). The upper and lower extreme values Gx_(MAX-U)and Gx_(MAX-L) are variable with variation of vehicle speed Vm.

In the embodiment just described, the parameter is in the form ofmaximum longitudinal acceleration Gx_(MAX) and it is used as a basis todetermine a target value P_(PB) of brake pressure.

With reference to FIGS. 17-18, in another preferred embodiment, theprocessor utilizes accelerator angle θ instead of longitudinalacceleration Gx to establish a maximum accelerator angle θ_(MAX). Theprocessor calculates a product θ_(MAX)×F (F is a speed ratio betweeninput shaft and an output shaft of transmission). This product θ_(MAX)×Fis used as a parameter instead of Gx_(MAX) in determining a base valueP_(PBO) of hydraulic brake pressure by referring to FIG. 18. FIG. 18 isanalogous to FIG. 12. The product θ_(MAX)×F exhibits a reasonably goodapproximation to maximum longitudinal acceleration Gx_(MAX) indetermining P_(PBO).

This embodiment is substantially the same as the embodiment describedparticularly with reference to FIGS. 7-15 except the use of informationto determine speed ratio F, main routine 400A (see FIG. 16), sub-routine440A (see FIG. 17), and a look-up table as illustrated in FIG. 18.

With reference to FIG. 16, the main routine 400A is used instead of themain routine 400 (see FIG. 9). The main routines 400A and 400 aresubstantially the same so that like reference numerals are used todesignate like process blocks throughout FIGS. 9 and 16. However, themain routine 400A has process blocks 402A, 404A, and 416A instead ofprocess blocks 402, 404, and 416 of the main routine 400.

FIGS. 16, 10 and 17 illustrate a series of operations for carrying outthe preferred embodiment of this invention. The process steps of FIGS.16, 10 and 17 are periodically executed in brake controller 46 whenstand-by braking mode is selected by SMMB switch 136 (see FIG. 7) afterthe ignition has been on and electric power has been applied tocontroller 46.

The process steps of FIGS. 16, 10 and 17 are carried out every ΔT (forexample, 10 milliseconds) in controller 46 as provided through astandard computer timer-based interrupt process.

Each sequential execution of the microprocessor operations of FIG. 16begins at “START” block and proceeds to process block 402A. In block402A, the processor inputs or receives output signals from sensors,including pressure sensor 128, AC sensor 134 and vehicle speed sensor138, from switches, including brake switch 132, SBBM switch 136, andfrom systems, including obstacle detection system 30, vehicle weightdetection system 140, road friction coefficient (μ) determining system150, road gradient (Rd) determining system 152 and transmissioncontroller 148. The determined value of accelerator angle θ is stored asthe newest one of a predetermined number of stored data after moving asequence of the stored data to the right or left by overflowing theoldest one of the stored data. In the embodiment, the predeterminednumber of stored data is forty and the forty stored data are representedby θ₀, θ₋₁, θ₋₂, . . . θ₋₃₉, respectively, where θ₀ represents thenewest stored datum, and θ₋₃₉ represents the oldest stored datum. Morespecifically, the determined value θ in the present operation cycle isstored as θ₀. The forty stored data are processed in block 404A. Inblock 404A, the processor carries out a standard process of selecting ordetermining the maximum among the forty stored data θ₀, θ₋₁, θ₋₂, . . .θ₋₃₉ to update a maximum accelerator angle θ_(MAX). Processing at block404A provides the maximum θ_(MAX) among forty sampled determined valuesof accelerator angle θ, which have been sampled over a period of time of400 milliseconds that ends with beginning of each sequential executionof the microprocessor operations. Description on microprocessoroperations at blocks 406, 408, 410, 412 and 414 is hereby omitted forbrevity. In query at block 414, if flag F_(PB) is set, the processproceeds to block 416A, and microprocessor operations 442, 444A, and448-464 of sub-routine 440A, as illustrated in FIG. 17, are carried out.In query at block 414, if flag F_(PB) is cleared or reset, the processproceeds to block 412, and processes to stop command are carried out.After block 416A or 412, the process skips to “RETURN” block in FIG. 16,

The sub-routine 440A of FIG. 17 is substantially the same as thesub-routine 440 of FIG. 11 except the provision of process block 444A inthe place of block 444.

Referring to FIG. 17, microprocessor operations at blocks 442, 444A,446-464 are carried out to determine a target value P_(PB) of brakepressure based on a parameter in the form of a product F×θ_(MAX), whichhas been established based on forty stored data θ₀, θ₋₁, θ₋₂, . . . θ₋₃₉sampled over a period of time of 400 milliseconds that ends withbeginning of execution of the microprocessor operations upondetermination at block 414 that operator braking action is imminent.More specifically, at process block 442, a stand-by braking start-upflag F_(ST) is checked. Flag F_(ST) set after execution of the initialoperation cycle of sub-routine 440A. In query at block 442, if flagF_(ST) is cleared or reset (answer “YES”), the process proceeds to block444A and a base value P_(PBO) of brake pressure is determined againstparameter θ_(MAX)×F and vehicle speed Vm. The process then proceeds toblock 446 and flag F_(ST) is set. The process proceeds next to block448. In query at block 442, if flag F_(ST) has been set (answer “NO”),the process skips to block 448. As flag F_(ST) is initially reset duringprocessing at block 444A, but it is set afterwards, the process skipsfrom block 442 to block 448 during each of the subsequent operationcycles of sub-routine 440A.

At process block 444A, an appropriate base value P_(PBO) of brake fluidis determined against parameter θ_(MAX)×F and vehicle speed Vm.

With reference to FIG. 18, description is made on how to determine, atblock 444A in the embodiment, an appropriate base value P_(PBO) usingparameter θ_(MAX)×F and vehicle speed Vm. FIG. 18 is a graph depicting afilter having various ranges of values of a parameter in the form ofproduct θ_(MAX)×F against various values of vehicle speed Vm. Lines S1and S2 illustrate variations of upper and lower extreme values of theranges of the filter. As indicated by lines S1 and S2, upper and lowerextreme values remain as high as θ_(MAX)×F_(Hi-U) and θ_(MAX)×F_(Hi-L),respectively, against various values of vehicle speed Vm lower than orequal to Vm_(Lo), while they remain as high as θ_(MAX)×F_(Lo-U) andθ_(MAX)×F_(Lo-L), respectively, against various values of vehicle speedVm higher than or equal to Vm_(Hi). Against intermediate values ofvehicle speed Vm between Vm_(Lo) and Vm_(Hi), the lines S1 and S2 haveramp-like sections, respectively, The ramp-like section of line S1interconnects a level as high as θ_(MAX)×F_(Hi-U) and a level as high asθ_(MAX)×F_(Lo-U). The ramp-like section line S2 interconnects a level ashigh as θ_(MAX)×F_(Hi-L) and a level as high as θ_(MAX)×F_(Lo-L). Therelationship is such that Vm_(Hi)>Vm_(Lo). The relationship is such that

θ_(MAX) ×F _(Hi-U)>θ_(MAX) ×F _(Hi-L)>θ_(MAX) ×F _(Lo-U)>θ_(MAX) ×F_(Lo-L,)

and

(θ_(MAX) ×F _(Hi-U)θ_(MAX) ×F _(Hi-L))>(θ_(MAX) ×F _(Lo-Lθ) _(MAX) ×F_(Lo-L))

As is readily seen from FIG. 18, the filter has a wide range, whichcovers relatively large values of parameter θ_(MAX)×F, when Vm is lessthan or equal to Vm_(Lo), while it has a narrow range, which coversrelatively small values of parameter θ_(MAX)×F, when Vm is greater thanor equal to Vm_(Hi). As Vm increases from Vm_(Lo) toward Vm_(Hi), therange of filter gradually becomes narrow and the coverage by the filterrange shifts.

If a determined value of parameter θ_(MAX)×F is greater than an upperextreme value, i.e., a point on line S1, selected against a determinedvalue of vehicle speed Vm, a maximum base value P_(PBO MAX) is set asbase value P_(PBO). If a determined value of parameter θ_(MAX)×F is lessthan a lower extreme value, i.e., a point on line S2, selected against adetermined value of vehicle speed Vm, a minimum base value P_(PBO MIN)is set as base value P_(PBO). In the embodiment, the setting is suchthat the maximum base value P_(PBO MAX) is 0.5 MPa and the minimum basevalue P_(PBO MIN) is 0.1 MPa.

Let us consider the case where a determined value of parameter θ_(MAX)×Fis less than or equal to an upper extreme value, i.e., a point on lineS1, selected against a determined value of vehicle speed Vm, but greaterthan or equal to a lower extreme value, i.e., a point on line S2,selected against the determined value of vehicle speed Vm. In this case,the base value P_(PBO) is determined by calculating the equation asfollows:

P _(PBO)=(P _(PB MAX) −P _(PB MIN))×(θ_(MAX) ×F−θ _(MAX) ×F_(-L))÷(θ_(MAX) ×F _(-U)−θ_(MAX) ×F _(-L))+P _(PB MIN)  (5),

where:

θ_(MAX)×F_(-U) is a general representation of an upper extreme value ofa range selected against a determined value of vehicle speed Vm;

θ_(MAX)×F_(-L) is a general expression of a lower extreme value of therange; and

θ_(MAX)×F* represents a determined value of maximum longitudinalacceleration that falls in the range having the upper and lower extremevalues θ_(MAX)×F_(-U) and θ_(MAX)×F_(-L).

In a stored look-up table in computer readable storage medium 104, upperand lower extreme values θ_(MAX)×F_(-U) and θ_(MAX)×F_(-L) are arrangedor allocated against various values of vehicle speed Vm in a manner asillustrated by the upper and lower threshold lines S1 and S2 illustratedin FIG. 18. In the embodiment, this look-up table is used formicroprocessor operations at block 444A in FIG. 17.

Referring back to FIG. 17, at block 444A, the processor determines basevalue P_(PBO) of brake pressure through microprocessor operations, whichinclude:

1) Performing a table look-up operation of the above-mentioned look-uptable using a determined value of vehicle speed Vm to find or determineupper and lower extreme values θ_(MAX)×F_(-U) and θ_(MAX)×F_(-L) of arange appropriate to the determined value of vehicle speed Vm;

2) Comparing a determined product θ_(MAX)×F to the determined upper andlower extreme values θ_(MAX)×F_(-U) and θ_(MAX)×F_(-L);

3) In the case (A*) where θ_(MAX)×F_(-U)≧θ_(MAX)×F≧θ_(MAX)×F_(-L),determining base value P_(PBO) by calculating the equation (5);

4) In the case (B*) where θ_(MAX)×F<θ_(MAX)×F_(-L), setting thatP_(PBO)=P_(PBO MIN); and

5) In the case (C*) where θ_(MAX)×F>θ_(MAX)×F_(-U), setting thatP_(PBO l =P) _(PBO MAX).

After microprocessor operations at block 444A, the process proceeds toblock 446 and then to block 448. Microprocessor operations at blocks448-464 are the same as those of sub-routine 440 of FIG. 11. Thus,description on them is hereby omitted for brevity.

In the embodiments of this invention, application of stand-by brakingtorque is terminated upon operator depression of brake pedal (see blocks462 and 464). If desired, application of stand-by braking torque maycontinue even after operator has depressed brake pedal.

In the embodiments of this invention, brake booster is utilized toregulate hydraulic brake pressure to accomplish a target value P_(PB) ofhydraulic brake pressure. This invention is not limited to this. Ifdesired, a system hydraulic fluid pressure discharged by a pump may beregulated to provide the target value P_(PB).

In the embodiments of this invention, a master cylinder is operated toproduce hydraulic brake pressure for application of braking torque. Thisinvention is not limited to this. If a powering system employs atraction motor/generator as a power source, a desired stand-by brakingtorque may be applied by regulating current passing through the motor.

While the present invention has been particularly described, inconjunction with preferred embodiments, it is evident that manyalternatives, modifications and variations will be apparent to thoseskilled in the art in light of the foregoing description. It istherefore contemplated that the appended claims will embrace any suchalternatives, modifications and variations as falling within the truescope and spirit of the present invention.

This application claims the priority of Japanese Patent Application No.2000-247161, filed Aug. 17, 2000, the disclosure of which is herebyincorporated by reference in its entirety.

What is claimed is:
 1. A method for controlling a stand-by brakingtorque applied to an automotive vehicle under a condition of approachingor following an obstacle preceding the vehicle, the automotive vehiclehaving a powering system for applying a driving torque to the vehicle inresponse to an operator power demand, the method comprising: determininga variable indicative of dynamic situation of the vehicle; sampling thedetermined values of the dynamic situation indicative variableimmediately before an operator braking action to reduce the speed of thevehicle is imminent; using the sampled values of the dynamic situationindicative variable as a basis to establish a parameter; and using theestablished parameter as a basis to determine a target value of stand-bybraking torque, which is to be applied when the operator braking actionto reduce the speed of the vehicle is imminent.
 2. A method as claimedin claim 1, wherein the powering system includes an engine with variousengine speeds and a transmission with various speed ratios between aninput member driven by the engine and an output member drivingly coupledwith at least one wheel of the vehicle, wherein a system for determininglongitudinal acceleration, which the vehicle is subject to, is employed,and wherein the dynamic situation indicative variable is the determinedlongitudinal acceleration.
 3. A system for controlling a stand-bybraking torque applied to an automotive vehicle under a condition ofapproaching or following an obstacle preceding the vehicle, theautomotive vehicle having a powering system for applying a drivingtorque to the vehicle in response to an operator power demand through anaccelerator pedal, the system comprising: a detection system fordetecting a distance between the vehicle and the obstacle preceding thevehicle; a sensor for detecting an operation parameter indicative ofvehicle speed of the automotive vehicle; a sensor for detecting adepressed angle of the accelerator pedal indicative of operator powerdemand; a system for determining a longitudinal acceleration to whichthe automotive vehicle is subject to; a braking system for applicationof braking toque to the vehicle in response to a brake signal; and acontroller for determining whether or not an operator braking action toreduce the speed of the vehicle is imminent under a condition ofapproaching or following an obstacle preceding the vehicle based on thedetected distance by the detection system, the vehicle speed, and theoperator power demand, determining a target value of hydraulic brakepressure for stand-by braking torque based on the determined value oflongitudinal acceleration before determination that the operator brakingaction is imminent, determining the brake signal for the determinedtarget value of hydraulic pressure, and applying the determined brakesignal to the braking system upon determination that the operatorbraking action is imminent.
 4. A system as claimed in claim 3, whereinthe controller samples the determined values of longitudinalacceleration for a predetermined period of time that ends with thedetermination that operator braking action is imminent and selects themaximum acceleration value among the sampled determined values oflongitudinal acceleration, whereby the selected maximum accelerationvalue is used as a basis to determine the target value of hydraulicbrake pressure.
 5. A system as claimed in claim 3, wherein, with thesame vehicle speed, the controller adjusts the target value of hydraulicbrake pressure such that the greater the determined value oflongitudinal acceleration is, the greater the determined target value ofhydraulic brake pressure.
 6. A system as claimed in claim 3, wherein thelongitudinal acceleration determining system samples the detected valuesof depressed angle of the accelerator pedal in determining values oflongitudinal acceleration.
 7. A system as claimed in claim 3, whereinthe controller adjusts the target value of hydraulic brake pressure suchthat the greater the vehicle speed is, the greater the target value ofhydraulic brake pressure is.
 8. A system as claimed in claim 3, whereina system for detecting a vehicle weight of the motor vehicle isemployed, and wherein the controller adjusts the target value ofhydraulic brake pressure such that the greater the detected vehicleweight is, the less the target value of hydraulic brake pressure is. 9.A system as claimed in claim 3, wherein there is employed a system fordetecting coefficient of friction between the road surface and the tireof at least one wheel of the automotive vehicle, and wherein thecontroller adjusts the target value of hydraulic brake pressure suchthat the less the detected coefficient of friction is, the less thetarget value of hydraulic brake pressure is.
 10. A system as claimed inclaim 3, wherein a system for detecting road gradient is employed, andwherein the controller adjusts the target value of hydraulic brakepressure such that, in the case where the detected road gradient ispositive, the greater the magnitude of detected road gradient is, thegreater the target value of hydraulic brake pressure is, and, in thecase where the detected road gradient is negative, the greater themagnitude of detected road gradient is, the less the target value ofhydraulic brake pressure is.
 11. A system as claimed in claim 3, whereinthe powering system includes an engine and a transmission with variousspeed ratios between an input member driven by the engine and an outputmember drivingly coupled with at least one wheel of the vehicle, whereinthere is employed a system for detecting a speed ratio of thetransmission, and wherein the controller adjusts the target value ofhydraulic brake pressure such that the less the detected speed ratio is,the less the target value of the hydraulic brake pressure is.
 12. Asystem as claimed in claim 3, wherein the powering system includes anengine and a transmission with various speed ratios between an inputmember driven by the engine and an output member drivingly coupled withat least one wheel of the vehicle, wherein there is employed a systemfor detecting a speed ratio of the transmission, wherein thelongitudinal acceleration determining system samples the detected valuesof depressed angle of the accelerator pedal and samples the detectedvalue of speed ratio and calculates a product of depressed angle of theaccelerator pedal and speed ratio in determining values of longitudinalacceleration.
 13. A system as claimed in claim 3, wherein the controlleruses the determined value of longitudinal acceleration and thedetermined value of vehicle speed to find a base value of the targetvalue of the hydraulic brake pressure, and corrects the base value witha vehicle weight of the vehicle, a coefficient of friction between theroad surface and the tire of at least one wheel of the vehicle, and aroad gradient of the road in determining the target value of hydraulicbrake pressure.
 14. A system as claimed in claim 13, wherein the basevalue falls in a band between a maximum base value of hydraulic brakepressure and a minimum base value of hydraulic brake pressure.
 15. Asystem as claimed in claim 3, wherein the longitudinal accelerationdetermining system samples the detected values of depressed angle of theaccelerator pedal and samples the detected value of speed ratio of atransmission of the powering system and calculates a product ofdepressed angle of the accelerator pedal and speed ratio in determiningvalues of longitudinal acceleration, and wherein the controller uses thecalculated value of product and the determined value of vehicle speed tofind a base value of the target value of the hydraulic brake pressure,and corrects the base value with a vehicle weight of the vehicle, acoefficient of friction between the road surface and the tire of atleast one wheel of the vehicle, and a road gradient of the road indetermining the target value of hydraulic brake pressure.
 16. A systemas claimed in claim 15, wherein the base value falls in a band between amaximum base value of hydraulic brake pressure and a minimum base valueof hydraulic brake pressure.
 17. A method for controlling a stand-bybraking torque applied to an automotive vehicle under a condition ofapproaching or following an obstacle preceding the vehicle, theautomotive vehicle having a powering system for applying a drivingtorque to the vehicle in response to an operator power demand through anaccelerator pedal, the method comprising: detecting a distance betweenthe vehicle and the obstacle preceding the vehicle; detecting anoperation parameter indicative of vehicle speed of the automotivevehicle; detecting a depressed angle of the accelerator pedal indicativeof operator power demand; determining a longitudinal acceleration towhich the automotive vehicle is subject to; applying braking toque tothe vehicle in response to a brake signal; determining whether or not anoperator braking action to reduce the speed of the vehicle is imminentunder a condition of approaching or following an obstacle preceding thevehicle based on the detected distance, the vehicle speed, and theoperator power demand; determining a target value of hydraulic brakepressure for stand-by braking torque based on the determined value oflongitudinal acceleration before determination that the operator brakingaction is imminent; determining the brake signal for the determinedtarget value of hydraulic pressure; and applying the determined brakesignal upon determination that the operator braking action is imminent.18. A system for controlling a stand-by braking torque applied to anautomotive vehicle under a condition of approaching or following anobstacle preceding the vehicle, the automotive vehicle having a poweringsystem for applying a driving torque to the vehicle in response to anoperator power demand through an accelerator pedal, the systemcomprising: means for detecting a distance between the vehicle and theobstacle preceding the vehicle; means for detecting an operationparameter indicative of vehicle speed of the automotive vehicle; meansfor detecting a depressed angle of the accelerator pedal indicative ofoperator power demand; means for determining a longitudinal accelerationto which the automotive vehicle is subject to; means for applyingbraking toque to the vehicle in response to a brake signal; means fordetermining whether or not an operator braking action to reduce thespeed of the vehicle is imminent under a condition of approaching orfollowing an obstacle preceding the vehicle based on the detecteddistance, the vehicle speed, and the operator power demand; means fordetermining a target value of hydraulic brake pressure for stand-bybraking torque based on the determined value of longitudinalacceleration before determination that the operator braking action isimminent; means for determining the brake signal for the determinedtarget value of hydraulic pressure; and means for applying thedetermined brake signal upon determination that the operator brakingaction is imminent.
 19. An automotive vehicle having a powering systemfor applying a driving torque to the vehicle in response to an operatorpower demand through an accelerator pedal, the automotive vehiclecomprising: a detection system for detecting a distance between thevehicle and the obstacle preceding the vehicle; a sensor for detectingan operation parameter indicative of vehicle speed of the automotivevehicle; a sensor for detecting a depressed angle of the acceleratorpedal indicative of operator power demand; a system for determining alongitudinal acceleration to which the automotive vehicle is subject to;a braking system for application of braking toque to the vehicle inresponse to a brake signal; and a controller for determining whether ornot an operator braking action to reduce the speed of the vehicle isimminent under a condition of approaching or following an obstaclepreceding the vehicle based on the detected distance by the detectionsystem, the vehicle speed, and the operator power demand, determining atarget value of hydraulic brake pressure for stand-by braking torquebased on the determined value of longitudinal acceleration beforedetermination that the operator braking action is imminent, determiningthe brake signal for the determined target value of hydraulic pressure,and applying the determined brake signal to the braking system upondetermination that the operator braking action is imminent.
 20. Acomputer readable storage medium having information stored thereonrepresenting instructions executable by a brake controller to controlstand-by braking torque, the computer readable storage mediumcomprising: instructions for determining a variable indicative ofdynamic situation of the vehicle; instructions for sampling thedetermined values of the dynamic situation indicative variableimmediately before an operator braking action to reduce the speed of thevehicle is imminent; instructions for establishing a parameter based onthe sampled values of the dynamic situation indicative variable; andinstructions for using the established parameter to determine a targetvalue of stand-by braking torque.